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TR6 TR6 Fuel Odor in the Brake Servo


Jedi Hopeful
Strange question but I have to ask it.

Just got off the the phone with a Servo rebuilder out of Chicago. He said that fuel odor was getting into the servo which was not compatible with the seals and caused a failure (I have heard of brake fluid doing that). It has a new Brake MC.

The Strombergs were not visually leaking external or into the vacuum lines and I could not smell fuel but it bugs me.

Any idea where the odor originated or other possible areas of concern. I rebuilt them last year when I restored the car.
The engine runs fine after warmup. It does require heavy choke on startup.



How can that be? The manifold is a vacuum - unless your car has a turbo or s/c...

That said, a PCV valve is cheap. You could always put one inline.


Great Pumpkin
I agree with Alan. If you had good brakes earlier on and I'm sure that you did, you pulled vacuum for the booster from the banjo fitting that derives it's vacuum source from the intake manifold. That is a pulling rather than a pushing or pressure source.

Maybe the heavy choking is allowing a great deal of raw gas to accumulate in the manifold passages? I had excessive oil in my original twin intake that was pulled from the un-baffled aluminum valve cover, but it never ended up in the booster.

That's interesting.


Did you ever have a lot of backfiring? Even for a short period of time?


Great Pumpkin - R.I.P
The check valve in the servo is bad. What happens is that the servo housing gets evacuated to match cruise manifold vacuum, then when you step on the throttle the intake manifold gets filled with fuel/air mixture at nearly ambient pressure. Without the check valve, the vacuum in the servo housing sucks fuel/air back into the housing.


Great Pumpkin
Duh, Paul!!! Brake booster theory 101. Shame on me for overlooking the obvious. Thank you Randall.


Great Pumpkin
That's the fitting on the intake that looks like a banjo. It provides vacuum for the emissions/carbs and brakes.


Brosky said:
That's the fitting on the intake that looks like a banjo. It provides vacuum for the emissions/carbs and brakes.

Which earlier cars did not have. So if you don't have it Dale, don't fret.
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